A bioreactor of the type presented here is known from European Patent EP1301583 B1 to the present applicant. The complete contents of the disclosure of EP 1301583 B1 with regard to the constructive design is incorporated herein by reference. This known bioreactor is constructed in the manner of a prefabricated garage and has a front and a back end. The complete front end is open and is closed by a flap-shaped gate in an airtight manner. Fresh biomass can be introduced through the gate into the bioreactor and used biomass discharged from the bioreactor through it. The used or spent biomass is composted in a customary manner. According to the governing German biowaste regulations (BioabfV), compost may be discharged on open spaces and green areas only if the biowaste is harmless with regard to diseases and phytohygiene. For example, weed seeds and phytopathogenic germs, such as fire blight pathogens, must be killed. In order to kill diseases, weed seeds and phytopathogenic germs, the temperature in the composted matter must be maintained at a certain temperature range for a given time. This increases the requirements on the care that must be taken during the composting. If biogas is already produced in a thermophilic range (temperature >55° C.), then less care must be taken during the subsequent composting of the spent biomass. However, there is the danger in the bioreactors known from EP1301583 B1 that the spent biomass will be re-contaminated as the bioreactor is discharged, and the spent biomass will have to be decontaminated before it is composted.
Starting from the bioreactor according to EP1301583 B1, the present invention has the objective of designing a bioreactor in which the danger of contamination of the spent biomass with regard to diseases and phytohygiene is considerably reduced. Furthermore, the invention has the objective of providing a method for operating such a bioreactor.